RV042, WRV54G, BEFVP41 VPN issues

I have a rather large VPN network with about 9 linksys VPN routers spread all over the state. i have a RV042 at where you would call the "server" with a dedicated T1 hooked up on one port and DSL on the other for emergency's. i have a RV042, WRV54g and multiple BEFVP41's (some version one some version 2) that are in gateway to gateway with the "server" RV042. the problem i am having is they are running a simple telnet type program and the VPN disconnects everybody at a location multiple times a day. but the internet stays up the whole time. they don't all disconnect at all the locations at the same time either, one location will go down a few times in one day and another location will go down a few times that same day.. but at different times. and what is worse is the disconections seems to get worse towards evening / night time to the point where even with just one person left connected, at 11:00 pm they get disconnected every 20 minutes or less. all the routers have latest firmware. the internet connection varies from location to location, cable, DSL, and a T1 at the "server" site. i'm running out of ideas =(

the MTU is set to default on all the routers. it is set to auto on the RV042 at the "server" location. most of the client locations are also set to auto, a few are set to 1492 (because there is no auto option)